The present invention relates to a piezoelectric device, an actuator employing the piezoelectric device, and an ink jet-recording head; and in particular to a piezoelectric device having an improved voltage withstandability, an actuator employing such a piezoelectric device and an ink-jet recording head.
Conventionally, a piezoelectric device, for which a piezoelectric film is sandwiched between a lower electrode and an upper electrode, is employed as a device for converting electric energy to mechanical energy. Such a piezoelectric device is used, for example, as an actuator for an ink-jet recording head. Specifically, an ink-jet recording head generally comprises: a head base in which are formed multiple separate ink channels, such as ink cavities and ink reservoirs; a vibration plate that is attached to the head base and that covers all the ink channels; and piezoelectric devices that are fixed to the portions of the vibration plate corresponding to the ink channels. The thus arranged ink-jet recording head applies an electric field to the piezoelectric devices and displaces them, and in this manner discharges ink, which is contained in the ink channels, from ink ejection ports formed on nozzle plates provided along the ink channels.
Each of the piezoelectric devices comprises a lower electrode, a piezoelectric film formed on the lower electrode, and an upper electrode formed on the piezoelectric film. The composition of the piezoelectric film is generally a binary system containing lead zirconate titanate (hereinafter referred to as PZT) as the primary element, or a ternary system for which a third element is added to the PZT of the binary system. Piezoelectric film having such a composition can be formed by the sputtering method, the sol-gel method, the laser ablation method or the CVD method.
However, for a conventional piezoelectric device no consideration is given to the enhancement of its voltage withstandability, and the insulation provided for the piezoelectric film may be destroyed by an electric field that is applied to the piezoelectric device. Further, no consideration is given to the relationship existing between the piezoelectric characteristic of the piezoelectric device (piezoelectric film) and the voltage withstandability. The criticality of these problems increases as the piezoelectric film becomes thinner.